A Cenozoic-Style Scenario for the End-Ordovician Glaciation

• Main Authors: Desrochers, André, Ghienne, Jean-François, Vandenbroucke, T.R.A., Achab, Aïcha, Dabard, Marie-Pierre, Al., Et
• Other Authors: Department of Earth Sciences Ottawa, University of Ottawa Ottawa, Institut de physique du globe de Strasbourg (IPGS), Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Géosystèmes - UMR 8217 (Géosystèmes), Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-Université de Lille, Sciences et Technologies, Géosciences Rennes (GR), Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), European Geoscience Union
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2015
• Subjects: [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Allo; Canada; Ice Sheet
• Online Access: https://hal-insu.archives-ouvertes.fr/insu-01137649

International audience The end-Ordovician (Hirnantian) was an enigmatic interval in the Phanerozoic, known for massive glaciationpotentially at elevated CO2 levels, biogeochemical cycle disruptions recorded as large isotope anomalies and adevastating extinction event. Such linkage of eustatic, biological and isotopic records to the climatically forceddevelopment of an ice sheet can only be contemplated within a framework of high-resolution sequence stratigraphythat integrates allo-, chemo- or biostratigraphic markers. We develop sequence stratigraphic correlations fortwo superbly exposed and exceptionally well-developed latest Ordovician successions, the Anti-Atlas of Moroccoand Anticosti Island in Canada. Both offer sections, on a 100-km scale, from the basin edge to the axis of activesedimentary depocentres. Relative to the end-Ordovician ice-sheet centre (present-day north-central Africa), theyprovide a near-field (Anti-Atlas, siliciclastic platform) and a far-field (Anticosti Island, mixed carbonate and siliciclastic)stratigraphic records. These two successions, up to 300 and 100m thick, respectively, were deposited inbasins with notable subsidence rates and significant (ca. 100 m) initial water depths, enabling the development ofcomprehensive archives of the latest Ordovician glaciation. This framework, driven by glacio-eustatic cycles tiedto the evolution of polar continental-scale ice sheets over west Gondwana, enables the correlation of eustatic cyclesat a level that is beyond the resolution capability of most absolute dating methods and of biozones, the latter typicallyof Myr duration. A proposed Cenozoic-style scenario including three main glacial cycles and higher-orderphenomena necessitates the revision of the end-Ordovician, glaciation-related sequence of events.